In fact, the viscosity of engine oil is one of the most unobvious parameters, which often becomes a stumbling block when choosing an oil. The problem is that there are many different points of view – of salespeople, authorized service men, “garage” mechanics and simply experienced car owners. And these opinions often contradict one another. There is no dispute about one thing: If your car is seriously damaged, you need to come here:

In fact, if you understand at least in general the purpose of oil in the engine, the question of viscosity should not be too complicated.

Instead of an introduction:
The most popular misconceptions motorists have about engine oil viscosity, imposed by auto oil manufacturers and service station motorists:

“If I like to drive fast – standard engine oil is not good for me – you need to pour more sports car oils” – the real loss of power and rapid engine overhaul is ensured to you – act!
“When my engine was designed, there were no modern oils with high viscosity, so the car manufacturer could not recommend them” – not only were there no modern brands of motor oil, there were no technologies of engine production designed for modern motor oil, so start looking for a good master for the overhaul of your engine.

What is oil viscosity?

The main task of an auto oil is to prevent dry friction of the moving internal parts of the engine, as well as to provide minimum friction force with maximum tightness of the working cylinders. It is obvious that it is impossible to make a substance which would have the necessary properties for this, and at the same time would have stable characteristics in a wide range of temperatures, and the range of working temperatures of oil in the engine is wide enough.

It is necessary to note that the temperature that most motorists observe on the dashboard, and which is commonly referred to as the engine temperature – is actually the coolant temperature, which is really stable in the warmed engine and should be about 90 degrees. The oil temperature at the same time significantly “ranges” and can go up to 140-150 degrees, depending on the speed and intensity of driving.

On this basis, for each individual engine, the manufacturer defines compromise optimum parameters of a motor oil. Just these parameters, according to the engine manufacturer, should provide the maximum efficiency factor (efficiency factor) with the minimum wear and tear of the engine internal parts under given “typical” operating conditions.

The most important of automobile oil parameters is considered to be its viscosity.

In simple language, understandable to a motorist, it is possible to tell so: oil viscosity is its ability to remain on the surface of internal details of the engine and thus to keep fluidity. Doesn’t seem complicated? But it is the oil viscosity that changes most of all depending on the temperature, being a “variable” value?

That is why the American Association of Automotive Engineers (SAE) has developed the engine oil viscosity classification, which describes the viscosity of a particular motor oil at different operating temperatures. In essence, this classification gives the temperature range within which it is safe to run your engine, provided the engine manufacturer has approved an engine oil with these parameters for use in that engine.

What do the oil viscosity numbers on the label mean?

After the abbreviation SAE, we see several numbers separated by the letter W and a dash, for example 5W-30 (for all-season oil, which is usually used by all motorists). Without going into physics and complicated terminology (it is below), this inscription can be deciphered as follows:

5WThe oil viscosity coding is a low-temperature viscosity, which means that a cold start of the engine is possible at a temperature no lower than -35°C (i.e. you have to subtract 40 from the number before W). This is the minimum temperature of this motor oil, at which the engine oil pump can pump oil through the system, without dry friction of internal parts. This parameter has no effect on the operation of the warmed up engine.

If you subtract 35 from the same figure (in this case it is -30°C), we get the minimum temperature of engine “cranking”. Obviously, as the temperature goes down, the oil becomes thicker and it becomes more and more difficult for the starter to crank the engine during a cold start. But this is an average parameter, the real picture depends very much on the engine itself, and therefore it is very important when choosing a viscosity not to deviate from the recommendations of the manufacturer of your car.

That is all, the first number in front of W does not mean anything, and it has no effect on the operation of the warmed up engine. So if you live in the region where air temperature in winter seldom gets lower than -20°C – you are good for practically any oil you can buy by this parameter. But if your starter and battery are already a bit tired, it will certainly be easier to start the engine at -20°C with 0W-30 oil than with 15W-40.

Much more interesting is the second number in the designation – high-temperature viscosity (in this case it is 30). It is not so simple to translate it as the first one, for it is a composite index, specifying minimal and maximal oil viscosity at working temperatures of 100-150°C. The higher is this number, the higher is the viscosity of the engine oil at high temperatures. Whether this is good or bad for your engine, only the engine manufacturer knows.

What viscosity is better for my engine?

It is generally accepted that the higher the viscosity at high temperatures, the better. In particular, oils with a high value of high-temperature viscosity are recommended for sports cars. But it absolutely does not mean, that if you pour a sport oil into your civilian engine, it will become sport or it will go better. Most likely, it will be just the opposite – you will thus lose power and quickly lay down the engine.

I repeatThe recommendations about oil viscosity in the service book for the second time – in no case you should not pour into the engine the oil viscosity of which is not provided by the manufacturer of the car for your motor! The manufacturer has taken into account all possible driving conditions for your engine, and has recommended the viscosity parameters that are optimal for this particular engine.

Very revealing is the experiment conducted by Mikhail Kolodochkin and Alexander Shabanov, described in Za Rule magazine #3/2008. They tried to put into the engine of a VAZ eight with a high-temperature viscosity of 50 units and discovered (and proved) a significant drop in power, as well as increased engine wear, compared to the manufacturer’s intended engine oil with a top viscosity of 40 units.

Just don’t smile, saying: “ah, Zhiguli, well, it is clear…”. The experiment would give the same results on any foreign car, because the essence there is exactly what maximum viscosity the car manufacturer has provided!

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